The block gauge is a useful calibration tool in the industry and in the research institutes, for the measurement of dimensions. The conventional block gauges are usually prepared with metal materials as starting materials. These block gauges, however, inherit several disadvantages such as insufficient corrosion resistance and limited abrasion resistance. For these reasons, the maintenance and the storage of the block gauges requires considerably special cares. For example, they can not be handled with bare hands so to avoid rusts caused by fingerprints. They must be stored in a corrosion-free environment, such as in a cabinet with controlled humidity, and shall be preserved in rust-preventing oil. Upon usage, the rust-preventing oil shall be removed following several tedious procedures. In the oil-removing processes, considerable cares must be applied. This is because, if during the procedure dusts are accidentally involved, the surface of the gauge will be abraded.
In case any of the above-said situation takes place, the surface of the metal gauge are impaired. They can no longer provide the function of precise indication of dimensions.
Block gauges made of ceramic materials can prevent several disadvantages of the metal gauges. Some of the prior art have disclosed the preparation of ceramic gauges. Among them, U.S. Pat. No. 5,272,120, and its corresponding Japanese patent No. 63188701, is a good example. As ceramic block gauges are concerned, the commercially available ones are made from conventional ceramics such as zirconium, alumina, silicon carbide, tungsten carbide or silicon nitride. Block gauges made from ceramic materials, however, inherent poor optical reflectivity. They can not provide the function of measurement or calibration with optical measurement tools such as the block gauge interferometer.
U.S. Pat. No. 5,470,807 disclosed a block gauge comprising a composite of tungsten carbide and reinforced chromium carbide matrix. The block gauge prepared according to the '807 invention possesses the hardness, corrosion resistance and abrasion resistance of the ceramics and the optical reflectivity resembling that of the metal materials. This invention overcomes the disadvantages of both the ceramic and the metal materials.
According to the International Standard Organization ISO 3650-1978, Guide for Gauge Blocks, it is provided that a block gauge shall be legibly and permanently marked with its nominal size, grade and trademark. Marking for a block gauge made from a ceramic material is traditionally conducted by a protrusive approach such as painting or a recessed approach such laser radiating. Both are known to the public.
Painting is an easier approach in marking on a ceramic block gauge, in comparison with the laser radiating approach. In marking by painting, a protrusion of a painting materials to the surface of a block gauge produces same effects as as the corrosion on a metal block gauge. Furthermore, the protrusive marking paint can be easily ablated under normal application conditions. Therefore, painting can not satisfy the criterion of the .dagger-dbl.permanent.dagger-dbl. requirement in said ISO Guide.
The laser radiating approach involves a transient laser beam of high power being applied to etch some parts of the surface of the block gauge. The laser beam will induce a temporary, high temperature and localized heating on the surface of the target. Therefore, microcracks or microchippings on the surroundings of the radiated area may be found after the laser beam source is removed. These microcrackings and microchippings resulted from the rapid heating and quenching processes are the major reasons which cause the severe degrading of the mechanical behaviors of the bulk ceramic materials of the block gauge. Nevertheless, the microchippings will blemish the contour of the markings and blur the outlook of the marks on the block gauges. These damages are greatly exaggerated if the block gauge is made from composite materials.
It is thus an urgent need for the industry to have a novel method of marking the block gauge of ceramic composites.